Efficient srs resource indication methods

ABSTRACT

A method of identifying reference signal resources to be used in a transmission by a wireless device is disclosed. The method comprises a wireless device receiving signaling configuring the wireless device with a plurality of reference signal resource groups, each group comprising a plurality of reference signal resources. The wireless device subsequently receives an indication, in a control channel, of a selection of reference signal resources to be used. Each of the plurality of reference signal resources to be used is selected from a different one of the plurality of reference signal resource groups such that reference signal resources belonging to the same reference signal resource group are not selected for simultaneous use. A reference signal is then transmitted to a network node in the network using the indicated selection of reference signal resources.

This application is a continuation of U.S. application Ser. No.16/195,959, filed Nov. 20, 2018, which is a continuation ofInternational Application No. PCT/IB2018/057656, filed Oct. 2, 2018,which claims the benefit of U.S. Provisional Application No. 62/567,156,filed Oct. 2, 2017, the disclosures of which are fully incorporatedherein by reference.

TECHNICAL FIELD

The disclosed subject matter relates generally to telecommunications andmore particularly to efficient indication of SRS resources in a nextgeneration mobile wireless communication system.

BACKGROUND

The next generation mobile wireless communication system (5G or NR),will support a diverse set of use cases and a diverse set of deploymentscenarios. The later includes deployment at both low frequencies (100sof MHz), similar to LTE today, and very high frequencies (mm waves inthe tens of GHz). At high frequencies, propagation characteristics makeachieving good coverage challenging. One solution to the coverage issueis to employ high-gain beamforming, typically in an analog manner, inorder to achieve satisfactory link budget. Beamforming will also be usedat lower frequencies (typically digital beamforming), and is expected tobe similar in nature to the already standardized 3GPP LTE system (4G).

Moreover, it is expected that large parts of future NR networks will bedeployed for TDD. One benefit with TDD (compared to FDD) is that TDDenables reciprocity based beamforming, which can be applied both at theTRP (i.e. for DL) and the UE (i.e. for UL). For reciprocity based DLtransmission it is expected that the UE will transmit Sounding ReferenceSignals (SRSs) which the TRP will use to estimate the channel betweenthe TRP and UE. The channel estimate will then be used at the TRP tofind optimal precoding weights for the coming DL transmission, forexample by using eigenbeamforming. In similar way, it is expected thatCSI-RS will be used as sounding signal for reciprocity based ULtransmissions. It has been agreed in NR that a TRP can indicate a quasico-location (QCL) assumption to an earlier transmitted DL referencesignal (e.g. CSI-RS) that a UE may use when determining UL precoding.

Codebook-Based Precoding

Multi-antenna techniques can significantly increase the data rates andreliability of a wireless communication system. The performance is inparticular improved if both the transmitter and the receiver areequipped with multiple antennas, which results in a multiple-inputmultiple-output (MIMO) communication channel. Such systems and/orrelated techniques are commonly referred to as MIMO.

The NR standard is currently being specified. A core component in NR isthe support of MIMO antenna deployments and MIMO related techniques. Itis expected that NR will support uplink MIMO with at least 4 layerspatial multiplexing using at least 4 antenna ports with channeldependent precoding. The spatial multiplexing mode is aimed for highdata rates in favorable channel conditions. An illustration of thespatial multiplexing operation is provided in FIG. 4 for where CP-OFDMis used on the uplink.

As seen, the information carrying symbol vector s is multiplied by anN_(T)×r precoder matrix W, which serves to distribute the transmitenergy in a subspace of the N_(T) (corresponding to N_(T) antenna ports)dimensional vector space. The precoder matrix is typically selected froma codebook of possible precoder matrices, and typically indicated bymeans of a precoder matrix indicator (PMI), which specifies a uniqueprecoder matrix in the codebook for a given number of symbol streams.The r symbols in s each correspond to a layer and r is referred to asthe transmission rank. In this way, spatial multiplexing is achievedsince multiple symbols can be transmitted simultaneously over the sametime/frequency resource element (TFRE). The number of symbols r istypically adapted to suit the current channel properties.

LTE and NR uses OFDM in the downlink and hence the received N_(R)×1vector y_(n) for a certain TFRE on subcarrier n (or alternatively dataTFRE number n) is thus modeled by

y _(n) =H _(n) Ws _(n) +e _(n)

where e_(n) is a noise/interference vector obtained as realizations of arandom process. The precoder implemented by precoder matrix, W, can be awideband precoder, which is constant over frequency, or frequencyselective.

The precoder matrix is often chosen to match the characteristics of theN_(RX)N_(T) MIMO channel matrix H_(n), resulting in so-called channeldependent precoding. This is also commonly referred to as closed-loopprecoding and essentially strives for focusing the transmit energy intoa subspace which is strong in the sense of conveying much of thetransmitted energy to the UE. In addition, the precoder matrix may alsobe selected to strive for orthogonalizing the channel, meaning thatafter proper linear equalization at the UE, the inter-layer interferenceis reduced.

One example method for a UE to select a precoder matrix W can be toselect the W_(k) that maximizes the Frobenius norm of the hypothesizedequivalent channel:

$\max\limits_{k}{{{\hat{H}}_{n}W_{k}}}_{F}^{2}$

where

Ĥ_(n) is a channel estimate, possibly derived from CSI-RS as describedfurther below,

W_(k) is a hypothesized precoder matrix with index k, and

Ĥ_(n)W_(k) is the hypothesized equivalent channel.

In closed-loop precoding for the NR uplink, the TRP transmits, based onchannel measurements in the reverse link (uplink), TPMI to the UE thatthe UE should use on its uplink antennas. The gNodeB configures the UEto transmit SRS according to the number of UE antennas it would like theUE to use for uplink transmission to enable the channel measurements. Asingle precoder that is supposed to cover a large bandwidth (widebandprecoding) may be signaled. It may also be beneficial to match thefrequency variations of the channel and instead feed back afrequency-selective precoding report, e.g. several precoders and/orseveral TPMIs, one per subband.

Other information than TPMI is generally used to determine the UL MIMOtransmission state, such as SRS resource indicators (SRIs) as well astransmission rank indicator (TRIs). These parameters, as well as themodulation and coding state (MCS), and the uplink resources where PUSCHis to be transmitted, are also determined by channel measurementsderived from SRS transmissions from the UE. The transmission rank, andthus the number of spatially multiplexed layers, is reflected in thenumber of columns of the precoder W. For efficient performance, it isimportant that a transmission rank that matches the channel propertiesis selected.

Non-Codebook Based UL Transmission

In addition to codebook-based UL transmission, it has been agreed thatNR will support a non-codebook based transmission modes, which isapplicable when TX/RX reciprocity holds at the UE. In the codebook-basedmode, as stated earlier, the UE typically transmits a non-precoded SRSto sound the uplink channel and the gNB determines a preferred precoderfrom the codebook based on the SRS channel estimates and instructs theUE to apply said precoder on the PUSCH transmission by means of a TPMIcomprised in the UL grant.

For non-codebook based UL transmission however, the UE itself determinesone or more precoder candidates and uses said precoder candidates toprecode one or more SRS in one or more SRS resources. The gNBcorrespondingly determines one or more preferred SRS resource andinstructs the UE to use the precoder(s) applied for precoding the one ormore preferred SRS resources also for the PUSCH transmission. Thisinstruction may be signaled in the form of one or more SRI(s) comprisedin the DCI carrying the UL grant, but may alternatively or additionallyinclude TRI signaling.

For the UE to determine the UL precoder candidates, it needs to measurea DL reference signal, such as a CSI-RS in order to attain a DL channelestimate. Based on this DL channel estimate, and assuming TX/RXreciprocity holds, the UE can convert the DL channel estimate into an ULchannel estimate and use the UL channel estimate to determine a set ofUL precoder candidates, for instance by performing a singular valuedecomposition (SVD) of the UL channel estimate or by other establishedprecoder determination methods. Typically, the gNB would configure theUE, implicitly or explicitly, with which CSI-RS resource it can use toaid precoder candidate determination. In some proposals for NR, this isdone by indicating that a certain CSI-RS resource is reciprocallyspatially quasi co-located with the SRS resource(s) the UE is scheduledto use for UL sounding, for instance as a part of RRC configuration.

SRS Transmission Setting

How the SRS transmission should be done, for example which SRS resourceto use, the number of ports per SRS resource, etc, needs to be signaledto the UE from the TRP. One way to solve this (in a low overhead way) isto pre-define a set of “SRS transmission settings” using higher layersignaling (e.g. RRC) and then indicate in DCI which “SRS transmissionsetting” that the UE should apply. An “SRS transmission setting” can forexample contain information regarding which SRS resources and SRS portsthat the UE should use in the coming SRS transmission.

Exactly how SRS transmissions are configured and triggered for NR isstill under discussion, a text proposal to 3GPP Technical Specification38.331 defining the SRS related parameters are given in FIG. 24.

As shown in FIG. 24, the SRS-Config IE is used to configure soundingreference signal transmissions. The configuration defines a list ofSRS-Resources and a list of SRS-ResourceSets. Each resource set definesa set of SRS-Resources. The network triggers the transmission of the setof SRS-Resources using a configured aperiodicSRS-ResourceTrigger (thatis carried in physical layer downlink control information, ‘L1 DCI’).

Thus, the RRC configuration of “SRS transmission settings” are done withthe IE SRS-Config, which contains a list of SRS-Resources (the listconstitutes a “pool” of resources) wherein each SRS resource containsinformation of the physical mapping of the reference signal on thetime-frequency grid, time-domain information, sequence IDs, etc. TheSRS-Config also contains a list of SRS resource sets, which contains alist of SRS resources and an associated DCI trigger state. Thus, when acertain DCI state is triggered, it indicates that the SRS resources inthe associated set shall be transmitted by the UE.

UL Beam Management

Concepts for UL beam management (i.e. beam management based on ULreference signals) are currently being developed for NR to control thebeam (or more correctly the effective antenna pattern) for a respectiveUE panel. It is expected that UL beam management is performed by lettingthe UE transmit different SRS resources in different UE panel beams,which the TRP performs RSRP measurements on and signals back the SRI(s)corresponding to the SRS resource(s) with highest RSRP value(s). If amulti-panel UE is scheduled for SRS transmission of multiple beams fromeach of the multiple panels, the TRP and UE need to have a mutualagreement of which combinations of SRS resources can be transmittedsimultaneously from the different panels. Otherwise the TRP could selectSRS resources that could not be transmitted simultaneously, such as whenthe SRS resources correspond to different switched analog beams in thesame panel. The following note to the agreement from RAN1#90 forsignaling multiple SRIs (below) addresses this issue but does notconclude on how it should be done. Note: The gNB should only signalSRI(s) such that the UL precoding transmission inferred from thesignaled SRI(s) can be simultaneously conducted by the UE.

SUMMARY

To address the foregoing problems with existing approaches, disclosed isa method of identifying reference signal resources to be used in atransmission by a wireless device. The method comprises a wirelessdevice or UE receiving signaling configuring the wireless device with aplurality of reference signal resource groups, each group comprising aplurality of reference signal resources. The wireless devicesubsequently receives an indication, in a control channel (e.g., PDCCH),of a selection of reference signal resources to be used. Each of theplurality of reference signal resources to be used is selected from adifferent one of the plurality of reference signal resource groups suchthat reference signal resources belonging to the same reference signalresource group are not selected for simultaneous use. A reference signalis then transmitted to a network node in the network using the indicatedselection of reference signal resources.

In certain embodiments, the reference signal resources are soundingreference signal (SRS) resources and the transmitted reference signal isan SRS. Moreover, in certain embodiments, the reference signal istransmitted for purposes of beam management. The wireless device mayinclude multiple antenna panels, where each of the plurality ofreference signal resource groups corresponds to a different one of theantenna panels.

In certain embodiments, the indication of the plurality of referencesignal resources to be used includes a bit field, the length of the bitfield depending on a maximum number of MIMO layers that the wirelessdevice is configured to transmit and a number of reference signalresources in a corresponding one of the reference signal resourcegroups. For example, the length of the bit field may be sufficient toindicate S combinations of SRS resources, wherein S=Σ_(L=1) ^(L) ^(max)(_(L) ^(N)), and where Lmax is a maximum number of MIMO layers that thewireless device is configured to transmit and N is the number ofresources in the first reference signal resource group.

In another embodiment, the method for identifying a plurality of SRSresources to be used in a transmission by the wireless device includesreceiving signaling configuring the wireless device with a plurality ofSRS resources, receiving an indication, in a physical layer downlinkcontrol channel, of SRS resources to be used, and determining from theindication at least a first and a second SRS resource out of theplurality of SRS resources that should be used in a transmission. Inthis embodiment, the first and second SRS resources are permitted to beany of the plurality of the SRS resources, except where the first andsecond SRS resources are the same. The wireless device may then transmitat least one of: SRSs identified by the first and second SRS resource,and first and second MIMO layers that are mapped to the first and secondSRS resources, respectively.

In certain embodiments, determining the at least first and second SRSresources includes identifying the first and second SRS resources fromamong the plurality of SRS resources by a first and second index,respectively. Moreover, the first and second indexes further indicate anorder in which the first and second SRS resources are to be mapped tothe first and second MIMO layers. For example, the first and second MIMOlayers may be ranked by quality such that the first MIMO layer is ofhigher quality than the second MIMO layer and the first MIMO layer ismapped to by a lower one of the first and second indexes (or,alternatively, the first MIMO layer is mapped to a higher one of thefirst and second indexes).

In certain embodiments, the wireless device determines the first andsecond SRS resources using a table. The table may include only one entryfor each possible ordering of a combination of SRS resources, therebyrestricting the total number of selectable SRS resource combinations.

Also disclosed is a method for configuring and indicating use ofreference signal transmission settings in a wireless device operable ina wireless communication network. The method may be implemented by anetwork node, such as a base station. The method includes transmittingsignaling configuring the wireless device with a plurality of referencesignal resource groups, each group comprising a plurality of referencesignal resources (e.g., SRS resources). The method further includestransmitting an indication, in a control channel, of a selection ofreference signal resources to be used, wherein the network node selectseach of the plurality of reference signal resources to be used from adifferent one of the plurality of reference signal resource groups suchthat reference signal resources belonging to the same reference signalresource group are not selected for simultaneous use. The method furtherincludes receiving a reference signal (e.g., an SRS) from the wirelessdevice using the indicated selection of reference signal resources.

Also disclosed is a wireless device comprising processing circuitryconfigured to perform the steps of any one of the foregoing embodiments.

According to another embodiment, a network node (e.g., base station)implements a method that comprises transmitting signaling configuringthe wireless device with a plurality of SRS resources. The methodfurther includes transmitting an indication, in a physical layerdownlink control channel, of SRS resources to be used in a transmission,the SRS resources including at least a first and a second SRS resourceout of the plurality of SRS resources. The first and second SRSresources are permitted to be any of the plurality of the SRS resources,except where the first and second SRS resources are the same. The methodfurther includes receiving at least one of: SRSs identified by the firstand second SRS resource, and first and second MIMO layers that aremapped to the first and second SRS resources, respectively.

Also disclosed is a wireless device comprising processing circuitryconfigured to perform the steps of any one of the foregoing embodiments.

Also disclosed is a network node comprising processing circuitryconfigured to perform the steps of any one of the foregoing methodsimplemented in a network node.

Technical advantages of the foregoing embodiments include a reducednumber of possible reference signal resource indicator states and hencesignaling overhead is reduced based on the fact that reference signalresources belonging to the same reference signal resource group cannotbe selected simultaneously by a transmission point (e.g., network nodeor base station).

Reduced downlink control channel overhead for reference signal resourceindicator signaling may be achieved in, for example, multi-panel UEsperforming UL beam management, and/or when using non-codebook based ULMIMO transmission. Some embodiments further allow a flexible mapping ofSRS resources to MIMO layers in order to control the quality of thelayers. Other embodiments have reduced flexibility to map SRS resourcesto MIMO layers, while using less downlink control channel overhead.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate selected embodiments of the disclosed subjectmatter. In the drawings, like reference labels denote like features.

FIG. 1 is a diagram illustrating a wireless communication network.

FIG. 2 is a diagram illustrating a wireless communication device.

FIG. 3 is a diagram illustrating a radio access node.

FIG. 4 is a functional block diagram of a spatial multiplexingoperation.

FIG. 5 is a graphical illustration of an example wireless device withtwo panels and corresponding SRS resource groups.

FIG. 6 is a table with an example mapping between different SRI statesand corresponding SRI signaling bits for the wireless device shown inFIG. 5.

FIG. 7 is a table with an example set of different SRI group indices andcorresponding binary and decimal representations of the SRI groupindices.

FIG. 8 is an example set of SRI indication bits indicating four SRSresources in four corresponding SRS resource groups.

FIG. 9 is a flowchart illustrating a method of operating a wirelessdevice.

FIG. 10 is a diagram illustrating a virtual wireless device embodiment.

FIG. 11 is a flowchart illustrating a method of operating a networknode.

FIG. 12 is a graphical illustration of a virtual network node apparatusembodiment.

FIG. 13 is a flowchart illustrating another method of operating awireless device.

FIG. 14 is a graphical illustration of another virtual wireless deviceapparatus embodiment.

FIG. 15 is a flowchart illustrating another method of operating anetwork node.

FIG. 16 is a graphical illustration of another virtual network nodeapparatus embodiment.

FIG. 17 is a flowchart illustrating another method of operating anetwork node.

FIG. 18 is a graphical illustration of another virtual network nodeapparatus embodiment.

FIG. 19 is a graphical illustration of an example virtualizationenvironment in which embodiments of the invention may operate.

FIG. 20 is a graphical illustration of a telecommunication networkconnected via an intermediate network to a host computer in accordancewith some embodiments.

FIG. 21 is a graphical illustration of a host computer communicating viaa base station with a user equipment over a partially wirelessconnection in accordance with some embodiments.

FIG. 22 is a flowchart illustrating a method implemented in acommunication system including a host computer, a base station and auser equipment in accordance with some embodiments.

FIG. 23 is a flowchart illustrating another method implemented in acommunication system including a host computer, a base station and auser equipment in accordance with some embodiments.

FIG. 24 illustrates a sounding reference signal (SRS) configurationinformation element used to configure SRS resources in a wirelessdevice.

FIG. 25 illustrates an example operation of a digital precoder matrix ina wireless device.

DETAILED DESCRIPTION

The following description presents various embodiments of the disclosedsubject matter. These embodiments are presented as teaching examples andare not to be construed as limiting the scope of the disclosed subjectmatter. For example, certain details of the described embodiments may bemodified, omitted, or expanded upon without departing from the scope ofthe described subject matter.

Radio Node:

As used herein, a “radio node” is either a radio access node or awireless device.

Controlling Node:

As used herein, a “controlling node” either a radio access node or awireless device used to manage, control or configure another node.

Radio Access Node:

As used herein, a “radio access node” is any node in a radio accessnetwork of a cellular communications network that operates to wirelesslytransmit and/or receive signals. Some examples of a radio access nodeinclude, but are not limited to, a base station (e.g., an enhanced orevolved Node B (eNB) in a Third Generation Partnership Project (3GPP)Long Term Evolution (LTE) network or a gNB in a 3GPP NR network), a TRPin a distributed base station, a high-power or macro base station, alow-power base station (e.g., a micro base station, a pico base station,a home eNB, or the like), and a relay node.

Core Network Node:

As used herein, a “core network node” is any type of node in a CoreNetwork (CN). Some examples of a core network node include, e.g., aMobility Management Entity (MME), an Evolved-Serving Mobile LocationCenter (E-SMLC), a Packet Data Network (PDN) Gateway (P-GW), a ServiceCapability Exposure Function (SCEF), or the like.

Wireless Device:

As used herein, a “wireless device” is any type of device that iscapable of wirelessly transmitting and/or receiving signals to/fromanother wireless device or to/from a network node in a cellularcommunications network to obtain has access to (i.e., be served by) thecellular communications network. Some examples of a wireless deviceinclude, but are not limited to, a User Equipment (UE) in a 3GPPnetwork, a Machine Type Communication (MTC) device, an NB-IoT device, aFeMTC device, etc.

Network Node:

As used herein, a “network node” is any node that is either part of theradio access network or the CN of a cellular communicationsnetwork/system or a test equipment node.

Signaling:

As used herein, “signaling” comprises any of: high-layer signaling(e.g., via Radio Resource Control (RRC) or a like), lower-layersignaling (e.g., via a physical control channel or a broadcast channel),or a combination thereof. The signaling may be implicit or explicit. Thesignaling may further be unicast, multicast or broadcast. The signalingmay also be directly to another node or via a third node.

As discussed in the background section, if a multi-panel UE is scheduledfor SRS transmission of multiple beams from each of the multiple panels,the TRP and UE need to have a mutual agreement of which combinations ofSRS resources can be transmitted simultaneously from the differentpanels. Embodiments of the invention facilitate efficient signaling ofan indication of SRS resources to be used.

According to one embodiment, groups of SRS resources are identified,where only one of the resources in an SRS resource group can betransmitted at a time. The one resource from each of the SRS resourcegroups can be transmitted simultaneously with each of the other selectedSRS resources from the other groups. Given the knowledge of the numberof SRS resource groups, and which SRS resources are in the groups, theTRP can determine which SRS resources it can instruct the UE to transmitwhen multiple SRIs are signaled. One example will be given below:

Assume a UE with two panels (Panel A and Panel B), where each panel hasfour analog beams (A1-A4 and B1-B4), as illustrated in FIG. 5. The UEwill start with signaling to the TRP, in UE capabilities, that it hastwo SRS resource groups, where each SRS resources group consists of fourSRS resources. Then the TRP will configure the UE (using RRC signaling)with different SRS resource sets (as was described above). For example,one SRS resource set may consist of eight SRS resources, where SRSresources 1-4 belong to a first SRS resource group and SRS resource 5-8belong to a second SRS resource group. During a UE TX beam sweepprocedure, the TRP can trigger this SRS resource set (by an indicationin an aperiodic SRS transmission request) and the UE will know which SRSresources that should be transmitted on the same panel and which SRSresource that should be transmitted on different panels. The TRP canthen perform measurements on the eight transmitted SRS resources,determine the best SRS resource for each SRS resource group and signalthe corresponding SRIs back to the UE. Note that each SRS resource canconsist of one or several SRS ports, hence the procedure can be appliedfor both non-codebook based (single SRS port per SRS resource) andcodebook based UL transmissions (one or several SRS ports per SRSresource). However, note that, for non-codebook based UL transmissionwhere each SRS resource are allowed to be precoded over multiple antennaports, the SRS precoding in this case (i.e. when UL beam management ispresent) should not be applied over antenna ports belonging to differentpanels (because then the mutual agreement that certain SRS resource onlybelongs to a certain panel is broken).

In some embodiments, the number of possible SRI states and hence the SRIsignaling overhead is reduced based on the fact that SRS resourcesbelonging to the same SRS resource group cannot be selectedsimultaneously by the TRP. This can be done by RRC configuring a mappingbetween SRI signaling bits and the possible SRI states for SRS resourcesets that contains multiple SRS resource groups. In such embodiments,SRS groups may be selected from the total set of SRS groups configuredto a UE and SRS resources selected from the selected SRS groups.

In other embodiments, each of L_(max) SRS resources is selected from allof the remaining possible SRS resources in the SRS resources configuredto a UE, thereby allowing the SRS resources to be mapped to MIMO layersin a desired order.

In other embodiments, combinations of SRS resources are selectedaccording to a single fixed ordering method thereby using fewer bits forSRI signaling but not allowing arbitrary ordering of the SRS resource toMIMO layer mapping.

Reduced downlink control channel overhead for SRI signaling may beachieved in, for example, multi-panel UEs performing UL beam management,and/or when using non-codebook based UL MIMO transmission. Someembodiments further allow a flexible mapping of SRS resources to MIMOlayers in order to control the quality of the layers. Other embodimentshave reduced flexibility to map SRS resources to MIMO layers, whileusing less downlink control channel overhead.

In one example for “normal” SRS transmission (e.g. SRS transmission fornon-codebook based/codebook based UL transmission without UL beammanagement), the SRI signaling from the TRP can indicate to the UE whichSRS resources it should use for PUSCH transmission and the order inwhich they should be mapped to spatially multiplexed (‘MIMO’) PUSCHlayers. The signaling selects any one of the SRS resources to betransmitted on a first MIMO PUSCH layer, such as one that the gNB deemsto have the best quality (e.g. SINR, SINR, etc), then any SRS resourceof the remaining resources to be transmitted to a second MIMO PUSCHlayer that it deems to have the next best quality, and so on, until ithas selected L_(max) SRS resources in order of descending quality. Notethat in some embodiments, metrics other than quality may be used toselect the SRS resources. The total number of SRI states that need to besignaled to the UE in this embodiment is then: S_(T)=Σ_(L=1) ^(L) ^(max)S_(L), where S_(L)=N·(N−1)· . . . ·(N−(L−1)) or, equivalently,

${S_{L} = \frac{N!}{\left( {N - L} \right)!}},$

is the number of SKI states for a given number of layers L, N is thenumber of SRS resources in the triggered SRS resource set, L is a numberof SRS resources that can be triggered by SRI, and L_(max) is themaximum number of SRS resources the UE simultaneously can transmit on(i.e. for single SRS port SRS resources, L and L_(max) equal the numberof layers and the maximum number of layers, respectively, the UE can besignaled to transmit simultaneously). The large amount of possible SRIstates will lead to a large SRI overhead signaling. For example, assumethe number of SRS resources in the SRS resource set is equal to eightand the maximum number of PUSCH transmission layers equals to one or two(i.e. N=8; L=1 or 2), then the total possible number of SRI statesS_(T)=8+8·7=64. This means that 6 bits are required to indicate thechosen SRI state to the UE in this embodiment.

The order of the SRS resources with respect to the corresponding PUSCHMIMO layers may not be important, for example when a single channelcoded transport block is mapped across the MIMO layers and a singlemodulation and coding state is used (also known as ‘single codeword’MIMO transmission). Therefore, in an embodiment, the SRI signaling fromthe TRP to the UE consists of S_(T)=Σ_(L=1) ^(L) ^(max) S_(L)=Σ_(L=1)^(L) ^(max) (_(L) ^(N)) possible SRI states where

$\quad\begin{pmatrix}N \\k\end{pmatrix}$

is the number of combinations of N values taken k at a time, and N, L,and L_(max) are the same as defined above. In this embodiment with, N=8and L=1 or 2, then the total possible number of SRI states

$S_{T} = {{S_{1} + S_{2}} = {{\begin{pmatrix}8 \\1\end{pmatrix} + \begin{pmatrix}8 \\2\end{pmatrix}} = {{8 + 28} = 36.}}}$

This means that 6 bits are still required to indicate the chosen SRIstate to the UE. Similarly, if selection is restricted to only L=2 SRSresources, then the possible number of SRI states is

$S_{2} = {\begin{pmatrix}8 \\2\end{pmatrix} = 28.}$

This means that 5 bits are required to indicate the chosen SRI state tothe UE in this case.

Further reductions in SRI overhead are possible by taking into accountconstraints on SRS and/or PUSCH MIMO layer transmission. By way ofexample, assume there is a UE with two panels and four analog beams perpanels as illustrated in FIG. 5. In such case, many of the possible SRIstates will not be allowed because only one SRS resource from each SRSresource group can be selected. (Note that we use the term ‘SRS resourcegroup’ rather than ‘SRS resource set’ here to emphasize the constraintson SRS selection; both are a list of SRS resources configured to the UE,and an SRS resource set that is constrained in this way is equivalent toan SRS resource group) Hence, in this case it is preferred to do amapping between the possible SRI states and the SRI signaling bits inorder to reduce the overhead. In this example, L=2 SRS resources areselected: only one of A1-A4 beams in panel A and one out of B1-B4 beamsin panel B. Hence the total number of SRI states will be 4×4=16, whichwill require 4 SRI signaling bits (which is 20% reduction compared tothe example above that required 5 bits for L=2 selected SRS resources).FIG. 6 illustrates a table with the mapping between the different SRIstates and the SRI signaling bits.

More generally the formula for number of SRI states for an embodimentcan be written as S_(T)=Σ_(g=1) ^(N) ^(g) (Σ_(g=1) ^(N) ^(s)^((g))Π_(i∈G) _(k) M_(i)), where

${N_{s}(g)} = \begin{pmatrix}N_{g} \\g\end{pmatrix}$

states are used to select any of g SRS resource groups in a single,fixed, order, and Π_(i∈G) _(k) M_(i) states (each associated with an SRSresource group selection state) are used to select one SRS resource(corresponding to a beam) from each of the selected SRS resource groups,where M_(i) is the number of SRS resources (beams) for a selected SRSresource group with index i (corresponding to an i^(th) panel), G_(k) isa k^(th) set of indices of the selected SRS resource groups (i.e. G_(k)is a k^(th) subset of {1, 2, . . . , N_(g)} with g elements), and N_(g)is the total number of SRS groups (panels).

For simplification in signaling, one can assign states such that themaximum number of resources per resource group in any of the SRSresource groups configured to the UE, M_(max), is always assumed whencalculating SRI, and then the number of SRI states can be written as

$S_{T} = {\sum\limits_{g = 1}^{N}{\begin{pmatrix}N_{g} \\g\end{pmatrix}{\left( M_{{ma}\; x} \right)^{g}.}}}$

The single fixed order can be such that the combinations of SRS resourceindices selected by SRI are monotonically increasing such that the firstMIMO layer has the lowest SRS index, the second MIMO layer has the nextlowest SRS index, etc. Alternatively, the combinations of SRS resourceindices selected by SRI are monotonically decreasing such that the firstMIMO layer has the highest SRS index, the second MIMO layer has the nexthighest SRS index, etc.

In this embodiment, with N_(g)=2 resource groups and M_(i)=4 resourcesin each SRS resource group, and L_(max)=2, S_(T)=24 SRI states areneeded, and so 5 bits could be used to signal SRI to the UE in thisembodiment.

In some embodiments, the SRI can be encoded as the following:

SRI=Y(g ₁ ,g ₂ , . . . ,g _(L) _(max) )·(Π_(k=1) ^(L) M _(k))+(Σ_(l=1)^(L)(Π_(k=1) ^(l−1) M _(k))X _(l)),

where 0≤X_(l)<M₁ is the identifier of the SRS resource selected from theSRS resource group with index l, and Π_(k=1) ⁰M_(k) ≙1. The number ofselected SRS resource groups L and the value of Y( ) can correspond tothe selected SRS resource group indices {g₁, g₂, . . . , g_(L) _(max) }in a given row of a table, where L is the number of selected SRSresources. In the table in FIG. 7 for an example embodiment below,L_(max)=4 SRS resource groups are configured. The possible values of{g₁, g₂, . . . , g_(L) _(max) } are given as well as the correspondingvalues of L and Y(g₁, g₂, . . . , g_(L) _(max) ). In general, a tablefor a given value of L_(max) is constructed by first selecting eachpossible resource group of L_(max) SRS resource groups, then eachpossible pair of resource groups of L_(max) SRS resource groups, theneach possible combination of 3 resource groups of L_(max) SRS resourcegroups, and so on. The pairs and combinations are selected such that theindices of the selected resource groups follow a fixed order, such as amonotonically increasing order, and such that each pair or combinationonly appears once in the table.

In some embodiments, the number of layers L may be strictly less thanthe number of SRS resource groups configured to the UE, L_(max). In thiscase, the function Y(g₁, g₂, . . . , g_(L) _(max) ) that is constructedas described above and shown in the example table below can producevalues that can be encoded with a smaller number of bits than is neededfor when L≤L_(max). This can be seen in the table below by observingthat for L=1, values of Y(g₁, g₂, . . . , g_(L) _(max) ) are 3 or less,therefore taking 2 bits to encode, whereas with L≤4, 4 bits are needed.Therefore, in an embodiment, the size of the field used to signal SRI isdetermined according to the maximum number of MIMO layers that the UE isconfigured to transmit, the number of SRS resource groups from which anSRS resource may be selected, and the number of SRS resources in one ormore SRS groups.

In an alternative embodiment, the SRI is encoded directly as a bitstream rather than first being encoded as a decimal number and thenmapped to a number of bits in the DCI. If the number of SRS resourcesper SRS resource groups are powers of two, i.e. M₁=2^(m) ^(l) , thisembodiment is functionally equivalent to the previously discussedembodiment. For example, the binary representation of Y(g₁, g₂, . . . ,g_(L) _(max) ) may be mapped to the most significant bits, then thebinary representation of X₁ is mapped to the subsequent bits, then thebinary representation of X₂ and so forth until X_(L) is mapped to theleast significant bits. If L<L_(max), the bitstream is padded withzeroes to fill up the field size. An example of this bit mapping isgiven in FIG. 8, where 4 SRS resource groups, each comprising 4 SRSresources, are assumed.

The described embodiments may be implemented in any appropriate type ofcommunication system supporting any suitable communication standards andusing any suitable components. As one example, certain embodiments maybe implemented in an LTE network, such as that illustrated in FIG. 1.

Referring to FIG. 1, a radio access communication network 100 comprisesa plurality of wireless communication devices 105 (e.g., conventionalUEs, machine type communication [MTC]/machine-to-machine [M2M] UEs) anda plurality of radio access nodes 110 (e.g., eNodeBs or other basestations). Communication network 100 is organized into cells 115, whichare connected to a core network 120 via corresponding radio access nodes110. Radio access nodes 110 are capable of communicating with wirelesscommunication devices 105 along with any additional elements suitable tosupport communication between wireless communication devices or betweena wireless communication device and another communication device (suchas a landline telephone).

Although wireless communication devices 105 may represent communicationdevices that include any suitable combination of hardware and/orsoftware, these wireless communication devices may, in certainembodiments, represent devices such as an example wireless communicationdevice illustrated in greater detail by FIG. 2. Similarly, although theillustrated radio access node may represent network nodes that includeany suitable combination of hardware and/or software, these nodes may,in particular embodiments, represent devices such as the example radioaccess node illustrated in greater detail by FIG. 3.

Referring to FIG. 2, a wireless communication device 200 comprises aprocessor 205, a memory, a transceiver 215, and an antenna 220. Incertain embodiments, some or all of the functionality described as beingprovided by UEs, MTC or M2M devices, and/or any other types of wirelesscommunication devices may be provided by the device processor executinginstructions stored on a computer-readable medium, such as the memoryshown in FIG. 2. Alternative embodiments may include additionalcomponents beyond those shown in FIG. 2 that may be responsible forproviding certain aspects of the device's functionality, including anyof the functionality described herein.

Referring to FIG. 3, a radio access node 300 comprises a node processor305, a memory 310, a network interface 315, a transceiver 320, and anantenna 325. In certain embodiments, some or all of the functionalitydescribed as being provided by a base station, a gNodeB, an eNodeB,and/or any other type of network node may be provided by node processor305 executing instructions stored on a computer-readable medium, such asmemory 310 shown in FIG. 3. Alternative embodiments of radio access node300 may comprise additional components to provide additionalfunctionality, such as the functionality described herein and/or relatedsupporting functionality.

FIG. 9 is a flowchart illustrating a method 900 of operating a wirelessdevice (e.g., wireless communication device 105). The method 900comprises a step S905 in which signaling is received from a network nodein a wireless communications network, the signaling configuring thewireless device to use a plurality of reference signal resource groups,each group comprising a plurality of reference signal resources. Thesignaling may configure the wireless device to use the plurality ofreference signal resource groups in a provisional sense, i.e., to beused as indicated by a message in a subsequently received controlchannel.

The method further comprises a step S910 in which an indication isreceived in a control channel (e.g., physical layer downlink controlchannel) from the network node, the indication including an indicationof the reference signal resources to be used. Each of the referencesignal resources to be used may be restricted to being selected from adifferent one of the plurality of reference signal resource groups suchthat reference signal resources belonging to the same reference signalresource group are not selected for simultaneous use. For example, thereference signal resources to be used include first and second referencesignal resources selected only from a respective first and second one ofthe plurality of reference signal resource groups. The method 900further includes a step S915 of transmitting a reference signal to thenetwork node using the first and second reference signal resources.

In an alternative embodiment, the method 900 may further include stepsS911, S912, and S913 intermediate to steps S910 and S915 in which the UEmakes various determinations based on the indication received in stepS910. For example, in optional step S911 the wireless device determines,from the indication, a first and second reference signal resource group,wherein the reference signal resource groups are reference signalresource groups. In optional step S912, the wireless device determinesfrom the indication a first reference signal resource that is selectedonly from the first reference signal resource group and in optional stepS913, the wireless device determines from the indication a secondreference signal resource that is selected only from the secondreference signal resource group. Moreover, in an alternative embodiment,step S915 can include transmitting at least one of reference signalsidentified by the first and second reference signal resources, and firstand second MIMO layers mapped to the first and second reference signalresources, respectively.

In one embodiment, the reference signal resources are sounding referencesignal (SRS) resources. In one embodiment, the indication of theplurality of reference signal resources to be used includes a bit field,where the length of the bit field depends on a maximum number of MIMOlayers that the wireless device is capable of transmitting and a numberof reference signal resources in a corresponding one of the referencesignal resource groups. (When the wireless device is configured withuplink MIMO operation, the wireless device may also be configured totransmit the maximum number of MIMO layers that the wireless device iscapable of transmitting.) The length of the bit field is sufficient toindicate S combinations of SRS resources, wherein:

${S = {\sum\limits_{L = 1}^{L_{{ma}\; x}}\begin{pmatrix}N \\L\end{pmatrix}}},$

andwhere L_(max) is a maximum number of MIMO layers that the wirelessdevice is configured to transmit and N is the number of resources in thefirst reference signal resource group. In another embodiment, the bitfield size may be determined based on a maximum number of MIMO layersthat the wireless device is configured to transmit, a number of SRSresource groups from which an SRS resource may be selected, and a numberof SRS resources in the plurality of SRS resource groups.

In one embodiment, the reference signal is transmitted for purposes ofbeam management. Furthermore, in one embodiment, the wireless device mayinclude multiple antenna panels, each one of the plurality of referencesignal resource groups corresponding to a different one of the antennapanels.

FIG. 10 is a schematic block diagram of an apparatus 1000 in a wirelessnetwork (for example, the wireless network shown in FIG. 1). Theapparatus may be implemented in a wireless device (e.g., wireless device105 shown in FIG. 1). Apparatus 1000 is operable to carry out theexample method described with reference to FIG. 9 and possibly any otherprocesses or methods disclosed herein. For example, module S1005 maycarry out the functionality of step S905; module S1010 may carry out thefunctionality of step S910; optional module S1011 may carry out thefunctionality of optional step S911; optional module S1012 may carry outthe functionality of optional step S912; optional module S1013 may carryout the functionality of optional step S913; and module S1015 may carryout the functionality of step S915. It is also to be understood that themethod of FIG. 9 is not necessarily carried out solely by apparatus1000. At least some operations of the method can be performed by one ormore other entities.

FIG. 11 is a flowchart illustrating a method 1100 of operating a networknode. The method 1100 comprises a step S1105 in which a total number ofpossible reference signal states is determined, the determination beingbased on a grouping of reference signal resources into reference signalresource groups, the grouping being configured such that only onereference signal resource is selectable from each reference signalresource group for use in a transmission. The method further comprises astep S1110 in which a mapping of different combinations of referencesignal indication bits to respective ones of the possible referencesignal states is determined. The mapping is then signaled to thewireless device at step S1115 and one or more preferred reference signalresources for an UL transmission from a wireless device are determinedat step S1120. The method further comprises a step S11125 in whichreference signal indication bits that are mapped by the mapping to anSRI state corresponding to the one or more preferred reference signalresources are signaled to the wireless device.

FIG. 12 illustrates a schematic block diagram of a virtual apparatus1200 in a wireless network (for example, the wireless network shown inFIG. 1). The apparatus may be implemented in a network node (e.g.,network node 110 shown in FIG. 1). Apparatus 1200 is operable to carryout the example method described with reference to FIG. 11 and possiblyany other processes or methods disclosed herein. For example, moduleS1205 may carry out the functionality of step S1105; module S1210 maycarry out the functionality of step S1110; module S1215 may carry outthe functionality of step S1115; module S1210 may carry out thefunctionality of step S1110; module S1215 may carry out thefunctionality of step S1115; module S1220 may carry out thefunctionality of step S1120; and module S1225 may carry out thefunctionality of step S1125. It is also to be understood that the methodof FIG. 11 is not necessarily carried out solely by apparatus 1200. Atleast some operations of the method can be performed by one or moreother entities.

FIG. 13 is a flowchart illustrating another method 1300 of operating awireless device (e.g., wireless communication device 105). The method1300 comprises a step S1305 in which the wireless device receivessignaling configuring the wireless device with a plurality of SRSresources. The signaling configuring the wireless device with aplurality of SRS resources may also indicate groupings of the pluralityof SRS resources into a plurality of SRS resource groups, each groupcomprising a plurality of SRS resources and wherein the first and secondSRS resources are selected from the same SRS resource group. The methodfurther comprises a step S1310 in which the wireless device receives anindication, in a physical layer downlink control channel, of SRSresources to be used. The method further comprises a step S1315 in whichthe wireless device determines from the indication at least a first anda second SRS resource out of the plurality of SRS resources that shouldbe used in a transmission. According to predetermined SRS resourceselection rules, for example, the indicated and determined first andsecond SRS resources are permitted to be any of the plurality of the SRSresources, except where the first and second SRS resources are the same.For example, the wireless device may determine the first and second SRSresources using a predetermined table, where the table includes only oneentry for each possible ordering of a combination of SRS resources,thereby restricting the total number of selectable SRS resourcecombinations.

The method 1300 further comprises a step S1320 in which the wirelessdevice transmits SRSs identified by the first and second SRS resource,and/or first and second MIMO layers that are mapped to the first andsecond SRS resources, respectively. The determination of first andsecond SRS resources in step S1315 may include identifying the first andsecond SRS resources from among the plurality of SRS resources by afirst and second index, respectively, the first and second indexesfurther indicating an order in which the first and second SRS resourcesare to be mapped to the first and second MIMO layers. For example, thefirst and second MIMO layers are ranked by quality such that the firstMIMO layer is of higher quality than the second MIMO layer and the firstMIMO layer is mapped to by a lower one of the first and second indexes.Alternatively, the first MIMO layer may be mapped to by a higher one ofthe first and second indexes.

FIG. 14 illustrates a schematic block diagram of a virtual apparatus1200 in a wireless network (for example, the wireless network shown inFIG. 1). The apparatus may be implemented in a wireless device (e.g.,wireless device 105 shown in FIG. 1). Apparatus 1400 is operable tocarry out the example method described with reference to FIG. 13 andpossibly any other processes or methods disclosed herein. For example,module S1405 may carry out the functionality of step S1305; module S1410may carry out the functionality of step S1310; module S1415 may carryout the functionality of step S1315; and module S1420 may carry out thefunctionality of step S1320. It is also to be understood that the methodof FIG. 13 is not necessarily carried out solely by apparatus 1400. Atleast some operations of the method can be performed by one or moreother entities.

FIG. 15 is a flowchart illustrating a method 1500 of operating a networknode. The method 1500 comprises a step S1505 in which a network nodetransmits signaling configuring the wireless device with a plurality ofreference signal resource groups, each group comprising a plurality ofreference signal resources, e.g., sounding reference signal (SRS)resources. In one embodiment, the wireless device includes multipleantenna panels and each one of the plurality of reference signalresource groups corresponds to a different one of the antenna panels.The network node may be apprised of the number of multiple antennapanels and number of antennas on each panel, e.g., by a capabilitiesmessage transmitted in a control channel from the wireless device.

The method 1500 further includes a step S1510 in which the network nodetransmits an indication, in a control channel, of a selection ofreference signal resources to be used. In accordance with apredetermined rule, the network node selects each of the plurality ofreference signal resources to be used from a different one of theplurality of reference signal resource groups such that reference signalresources belonging to the same reference signal resource group are notselected for simultaneous use. The indication of the plurality ofreference signal resources to be used may include a bit field, thelength of the bit field depending on a maximum number of MIMO layersthat the wireless device is configured to transmit and a number ofreference signal resources in a corresponding one of the referencesignal resource groups. Moreover, the bit field may be of sufficientlength to indicate S combinations of SRS resources, wherein:

${S = {\sum\limits_{L = 1}^{L_{{ma}\; x}}\begin{pmatrix}N \\L\end{pmatrix}}},$

andwhere L_(max) is a maximum number of MIMO layers that the wirelessdevice is configured to transmit and N is the number of resources in thefirst reference signal resource group.

The method 1500 further includes a step S1515 in which the network nodereceives a reference signal (e.g., an SRS) from the wireless deviceusing the indicated selection of reference signal resources. In oneembodiment, the reference signal is received as part of a beammanagement procedure initiated by the network node or the wirelessdevice.

FIG. 16 illustrates a schematic block diagram of a virtual apparatus1600 in a wireless network (for example, the wireless network shown inFIG. 1). The apparatus may be implemented in a network node (e.g.,network node 110 shown in FIG. 1). Apparatus 1600 is operable to carryout the example method described with reference to FIG. 15 and possiblyany other processes or methods disclosed herein. For example, moduleS1605 may carry out the functionality of step S1505; module S1610 maycarry out the functionality of step S1510; and module S1615 may carryout the functionality of step S1515. It is also to be understood thatthe method of FIG. 15 is not necessarily carried out solely by apparatus1600. At least some operations of the method can be performed by one ormore other entities.

FIG. 17 is a flowchart illustrating a method 1700 of operating a networknode. The method 1700 comprises a step S1705 in which the network nodetransmits signaling configuring the wireless device with a plurality ofSRS resources. The signaling configuring the wireless device with aplurality of SRS resources may also indicate groupings of the pluralityof SRS resources into a plurality of SRS resource groups, each groupcomprising a plurality of SRS resources and wherein the first and secondSRS resources are selected from the same SRS resource group. The methodfurther comprises a step S1710 in which the network node transmits anindication, in a physical layer downlink control channel, of SRSresources to be used. The wireless device may determine from theindication at least a first and a second SRS resource out of theplurality of SRS resources that should be used in a transmission.According to predetermined SRS resource selection rules, for example,the indicated and determined first and second SRS resources arepermitted to be any of the plurality of the SRS resources, except wherethe first and second SRS resources are the same. For example, thewireless device may determine the first and second SRS resources using apredetermined table, where the table includes only one entry for eachpossible ordering of a combination of SRS resources, thereby restrictingthe total number of selectable SRS resource combinations.

The method 1700 further includes a step S1715 in which the network nodereceives SRSs identified by the first and second SRS resource, and/orfirst and second MIMO layers that are mapped to the first and second SRSresources, respectively. The indication of first and second SRSresources in step S1710 may identify the first and second SRS resourcesfrom among the plurality of SRS resources by a first and second index,respectively, the first and second indexes further indicating an orderin which the first and second SRS resources are to be mapped to thefirst and second MIMO layers. For example, the first and second MIMOlayers are ranked by quality such that the first MIMO layer is of higherquality than the second MIMO layer and the first MIMO layer is mapped toby a lower one of the first and second indexes. Alternatively, the firstMIMO layer may be mapped to by a higher one of the first and secondindexes.

FIG. 18 illustrates a schematic block diagram of a virtual apparatus1800 in a wireless network (for example, the wireless network shown inFIG. 1). The apparatus may be implemented in a network node (e.g.,network node 110 shown in FIG. 1). Apparatus 1800 is operable to carryout the example method described with reference to FIG. 17 and possiblyany other processes or methods disclosed herein. For example, moduleS1805 may carry out the functionality of step S1705; module S1810 maycarry out the functionality of step S1710; and module S1815 may carryout the functionality of step S1715. It is also to be understood thatthe method of FIG. 18 is not necessarily carried out solely by apparatus1800. At least some operations of the method can be performed by one ormore other entities.

Each virtual apparatus 1000, 1200, 1400, 1600, and 1800 may compriseprocessing circuitry, which may include one or more microprocessor ormicrocontrollers, as well as other digital hardware, which may includedigital signal processors (DSPs), special-purpose digital logic, and thelike. The processing circuitry may be configured to execute program codestored in memory, which may include one or several types of memory suchas read-only memory (ROM), random-access memory, cache memory, flashmemory devices, optical storage devices, etc. Program code stored inmemory includes program instructions for executing one or moretelecommunications and/or data communications protocols as well asinstructions for carrying out one or more of the techniques describedherein, in several embodiments. In some implementations, the processingcircuitry may be used to perform the functionality of any suitable unitsof apparatus 1000 or 1200 to perform corresponding functions accordingto one or more embodiments of the present disclosure.

The term unit may have conventional meaning in the field of electronics,electrical devices and/or electronic devices and may include, forexample, electrical and/or electronic circuitry, devices, modules,processors, memories, logic solid state and/or discrete devices,computer programs or instructions for carrying out respective tasks,procedures, computations, outputs, and/or displaying functions, and soon, as such as those that are described herein.

Operation in Virtualization Environments

FIG. 19 is a schematic block diagram illustrating a virtualizationenvironment 1900 in which functions implemented by some embodiments maybe virtualized. In the present context, virtualizing means creatingvirtual versions of apparatuses or devices which may includevirtualizing hardware platforms, storage devices and networkingresources. As used herein, virtualization can be applied to a node(e.g., a virtualized base station or a virtualized radio access node) orto a device (e.g., a UE, a wireless device or any other type ofcommunication device) or components thereof and relates to animplementation in which at least a portion of the functionality isimplemented as one or more virtual components (e.g., via one or moreapplications, components, functions, virtual machines or containersexecuting on one or more physical processing nodes in one or morenetworks).

In some embodiments, some or all of the functions described herein maybe implemented as virtual components executed by one or more virtualmachines implemented in one or more virtual environments 1900 hosted byone or more of hardware nodes 1930. Further, in embodiments in which thevirtual node is not a radio access node or does not require radioconnectivity (e.g., a core network node), then the network node may beentirely virtualized.

The functions may be implemented by one or more applications 1920 (whichmay alternatively be called software instances, virtual appliances,network functions, virtual nodes, virtual network functions, etc.)operative to implement some of the features, functions, and/or benefitsof some of the embodiments disclosed herein. Applications 1920 are runin virtualization environment 1900 which provides hardware 1930comprising processing circuitry 1960 and memory 1990. Memory 1990contains instructions 1995 executable by processing circuitry 1960whereby application 1920 is operative to provide one or more of thefeatures, benefits, and/or functions disclosed herein.

Virtualization environment 1900, comprises general-purpose orspecial-purpose network hardware devices 1930 comprising a set of one ormore processors or processing circuitry 1960, which may be commercialoff-the-shelf (COTS) processors, dedicated Application SpecificIntegrated Circuits (ASICs), or any other type of processing circuitryincluding digital or analog hardware components or special purposeprocessors. Each hardware device may comprise memory 1990-1 which may benon-persistent memory for temporarily storing instructions 1995 orsoftware executed by processing circuitry 1960. Each hardware device maycomprise one or more network interface controllers (NICs) 1970, alsoknown as network interface cards, which include physical networkinterface 1980. Each hardware device may also include non-transitory,persistent, machine-readable storage media 1990-2 having stored thereinsoftware 1995 and/or instructions executable by processing circuitry1960. Software 1995 may include any type of software including softwarefor instantiating one or more virtualization layers 1950 (also referredto as hypervisors), software to execute virtual machines 1940 as well assoftware allowing it to execute functions, features and/or benefitsdescribed in relation with some embodiments described herein.

Virtual machines 1940, comprise virtual processing, virtual memory,virtual networking or interface and virtual storage, and may be run by acorresponding virtualization layer 1950 or hypervisor. Differentembodiments of the instance of virtual appliance 1920 may be implementedon one or more of virtual machines 1940, and the implementations may bemade in different ways.

During operation, processing circuitry 1960 executes software 1995 toinstantiate the hypervisor or virtualization layer 1950, which maysometimes be referred to as a virtual machine monitor (VMM).Virtualization layer 1950 may present a virtual operating platform thatappears like networking hardware to virtual machine 1940.

As shown in FIG. 19, hardware 1930 may be a standalone network node withgeneric or specific components. Hardware 1930 may comprise antenna 19225and may implement some functions via virtualization. Alternatively,hardware 1930 may be part of a larger cluster of hardware (e.g. such asin a data center or customer premise equipment (CPE)) where manyhardware nodes work together and are managed via management andorchestration (MANO) 19100, which, among others, oversees lifecyclemanagement of applications 1920.

Virtualization of the hardware is in some contexts referred to asnetwork function virtualization (NFV). NFV may be used to consolidatemany network equipment types onto industry standard high volume serverhardware, physical switches, and physical storage, which can be locatedin data centers, and customer premise equipment.

In the context of NFV, virtual machine 1940 may be a softwareimplementation of a physical machine that runs programs as if they wereexecuting on a physical, non-virtualized machine. Each of virtualmachines 1940, and that part of hardware 1930 that executes that virtualmachine, be it hardware dedicated to that virtual machine and/orhardware shared by that virtual machine with others of the virtualmachines 1940, forms a separate virtual network elements (VNE).

Still in the context of NFV, Virtual Network Function (VNF) isresponsible for handling specific network functions that run in one ormore virtual machines 1940 on top of hardware networking infrastructure1930 and corresponds to application 1920 in FIG. 19.

In some embodiments, one or more radio units 19200 that each include oneor more transmitters 19220 and one or more receivers 19210 may becoupled to one or more antennas 19225. Radio units 19200 may communicatedirectly with hardware nodes 1930 via one or more appropriate networkinterfaces and may be used in combination with the virtual components toprovide a virtual node with radio capabilities, such as a radio accessnode or a base station.

In some embodiments, some signaling can be effected with the use ofcontrol system 19230 which may alternatively be used for communicationbetween the hardware nodes 1930 and radio units 19200.

Operation with Remote Host Computers

With reference to FIG. 20, in accordance with an embodiment, acommunication system includes telecommunication network 2010, such as a3GPP-type cellular network, which comprises access network 2011, such asa radio access network, and core network 2014. Access network 2011comprises a plurality of base stations 2012 a, 2012 b, 2012 c, such asNBs, eNBs, gNBs or other types of wireless access points, each defininga corresponding coverage area 2013 a, 2013 b, 2013 c. Each base station2012 a, 2012 b, 2012 c is connectable to core network 2014 over a wiredor wireless connection 2015. A first UE 2091 located in coverage area2013 c is configured to wirelessly connect to, or be paged by, thecorresponding base station 2012 c. A second UE 2092 in coverage area2013 a is wirelessly connectable to the corresponding base station 2012a. While a plurality of UEs 2091, 2092 are illustrated in this example,the disclosed embodiments are equally applicable to a situation where asole UE is in the coverage area or where a sole UE is connecting to thecorresponding base station 2012.

Telecommunication network 2010 is itself connected to host computer2030, which may be embodied in the hardware and/or software of astandalone server, a cloud-implemented server, a distributed server oras processing resources in a server farm. Host computer 2030 may beunder the ownership or control of a service provider, or may be operatedby the service provider or on behalf of the service provider.Connections 2021 and 2022 between telecommunication network 2010 andhost computer 2030 may extend directly from core network 2014 to hostcomputer 2030 or may go via an optional intermediate network 2020.Intermediate network 2020 may be one of, or a combination of more thanone of, a public, private or hosted network; intermediate network 2020,if any, may be a backbone network or the Internet; in particular,intermediate network 2020 may comprise two or more sub-networks (notshown).

The communication system of FIG. 20 as a whole enables connectivitybetween the connected UEs 2091, 2092 and host computer 2030. Theconnectivity may be described as an over-the-top (OTT) connection 2050.Host computer 2030 and the connected UEs 2091, 2092 are configured tocommunicate data and/or signaling via OTT connection 2050, using accessnetwork 2011, core network 2014, any intermediate network 2020 andpossible further infrastructure (not shown) as intermediaries. OTTconnection 2050 may be transparent in the sense that the participatingcommunication devices through which OTT connection 2050 passes areunaware of routing of uplink and downlink communications. For example,base station 2012 may not or need not be informed about the past routingof an incoming downlink communication with data originating from hostcomputer 2030 to be forwarded (e.g., handed over) to a connected UE2091. Similarly, base station 2012 need not be aware of the futurerouting of an outgoing uplink communication originating from the UE 2091towards the host computer 2030.

Example implementations, in accordance with an embodiment, of the UE,base station and host computer discussed in the preceding paragraphswill now be described with reference to FIG. 21. In communication system2100, host computer 2110 comprises hardware 2115 including communicationinterface 2116 configured to set up and maintain a wired or wirelessconnection with an interface of a different communication device ofcommunication system 2100. Host computer 2110 further comprisesprocessing circuitry 2118, which may have storage and/or processingcapabilities. In particular, processing circuitry 2118 may comprise oneor more programmable processors, application-specific integratedcircuits, field programmable gate arrays or combinations of these (notshown) adapted to execute instructions. Host computer 2110 furthercomprises software 2111, which is stored in or accessible by hostcomputer 2110 and executable by processing circuitry 2118. Software 2111includes host application 2112. Host application 2112 may be operable toprovide a service to a remote user, such as UE 2130 connecting via OTTconnection 2150 terminating at UE 2130 and host computer 2110. Inproviding the service to the remote user, host application 2112 mayprovide user data which is transmitted using OTT connection 2150.

Communication system 2100 further includes base station 2120 provided ina telecommunication system and comprising hardware 2125 enabling it tocommunicate with host computer 2110 and with UE 2130. Hardware 2125 mayinclude communication interface 2126 for setting up and maintaining awired or wireless connection with an interface of a differentcommunication device of communication system 2100, as well as radiointerface 2127 for setting up and maintaining at least wirelessconnection 2170 with UE 2130 located in a coverage area (not shown inFIG. 21) served by base station 2120. Communication interface 2126 maybe configured to facilitate connection 2160 to host computer 2110.Connection 2160 may be direct or it may pass through a core network (notshown in FIG. 21) of the telecommunication system and/or through one ormore intermediate networks outside the telecommunication system. In theembodiment shown, hardware 2125 of base station 2120 further includesprocessing circuitry 2128, which may comprise one or more programmableprocessors, application-specific integrated circuits, field programmablegate arrays or combinations of these (not shown) adapted to executeinstructions. Base station 2120 further has software 2121 storedinternally or accessible via an external connection.

Communication system 2100 further includes UE 2130 already referred to.Its hardware 2135 may include radio interface 2137 configured to set upand maintain wireless connection 2170 with a base station serving acoverage area in which UE 2130 is currently located. Hardware 2135 of UE2130 further includes processing circuitry 2138, which may comprise oneor more programmable processors, application-specific integratedcircuits, field programmable gate arrays or combinations of these (notshown) adapted to execute instructions. UE 2130 further comprisessoftware 2131, which is stored in or accessible by UE 2130 andexecutable by processing circuitry 2138. Software 2131 includes clientapplication 2132. Client application 2132 may be operable to provide aservice to a human or non-human user via UE 2130, with the support ofhost computer 2110. In host computer 2110, an executing host application2112 may communicate with the executing client application 2132 via OTTconnection 2150 terminating at UE 2130 and host computer 2110. Inproviding the service to the user, client application 2132 may receiverequest data from host application 2112 and provide user data inresponse to the request data. OTT connection 2150 may transfer both therequest data and the user data. Client application 2132 may interactwith the user to generate the user data that it provides.

It is noted that host computer 2110, base station 2120 and UE 2130illustrated in FIG. 21 may be similar or identical to host computer2030, one of base stations 2012 a, 2012 b, 2012 c and one of UEs 2091,2092 of FIG. 20, respectively. This is to say, the inner workings ofthese entities may be as shown in FIG. 21 and independently, thesurrounding network topology may be that of FIG. 20.

In FIG. 21, OTT connection 2150 has been drawn abstractly to illustratethe communication between host computer 2110 and UE 2130 via basestation 2120, without explicit reference to any intermediary devices andthe precise routing of messages via these devices. Networkinfrastructure may determine the routing, which it may be configured tohide from UE 2130 or from the service provider operating host computer2110, or both. While OTT connection 2150 is active, the networkinfrastructure may further take decisions by which it dynamicallychanges the routing (e.g., on the basis of load balancing considerationor reconfiguration of the network).

Wireless connection 2170 between UE 2130 and base station 2120 is inaccordance with the teachings of the embodiments described throughoutthis disclosure. One or more of the various embodiments improve theperformance of OTT services provided to UE 2130 using OTT connection2150, in which wireless connection 2170 forms the last segment. Moreprecisely, the teachings of these embodiments may improve latency, amongother things, and thereby provide benefits such as betterresponsiveness.

A measurement procedure may be provided for the purpose of monitoringdata rate, latency and other factors on which the one or moreembodiments improve. There may further be an optional networkfunctionality for reconfiguring OTT connection 2150 between hostcomputer 2110 and UE 2130, in response to variations in the measurementresults. The measurement procedure and/or the network functionality forreconfiguring OTT connection 2150 may be implemented in software 2111and hardware 2115 of host computer 2110 or in software 2131 and hardware2135 of UE 2130, or both. In embodiments, sensors (not shown) may bedeployed in or in association with communication devices through whichOTT connection 2150 passes; the sensors may participate in themeasurement procedure by supplying values of the monitored quantitiesexemplified above, or supplying values of other physical quantities fromwhich software 2111, 2131 may compute or estimate the monitoredquantities. The reconfiguring of OTT connection 2150 may include messageformat, retransmission settings, preferred routing etc.; thereconfiguring need not affect base station 2120, and it may be unknownor imperceptible to base station 2120. Such procedures andfunctionalities may be known and practiced in the art. In certainembodiments, measurements may involve proprietary UE signalingfacilitating host computer 2110's measurements of throughput,propagation times, latency and the like. The measurements may beimplemented in that software 2111 and 2131 causes messages to betransmitted, in particular empty or ‘dummy’ messages, using OTTconnection 2150 while it monitors propagation times, errors etc.

FIG. 22 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 20 and 21. Forsimplicity of the present disclosure, only drawing references to FIG. 22will be included in this section. In step 2210, the host computerprovides user data. In substep 2211 (which may be optional) of step2210, the host computer provides the user data by executing a hostapplication. In step 2220, the host computer initiates a transmissioncarrying the user data to the UE. In step 2230 (which may be optional),the base station transmits to the UE the user data which was carried inthe transmission that the host computer initiated, in accordance withthe teachings of the embodiments described throughout this disclosure.In step 2240 (which may also be optional), the UE executes a clientapplication associated with the host application executed by the hostcomputer.

FIG. 23 is a flowchart illustrating a method implemented in acommunication system, in accordance with one embodiment. Thecommunication system includes a host computer, a base station and a UEwhich may be those described with reference to FIGS. 20 and 21. Forsimplicity of the present disclosure, only drawing references to FIG. 23will be included in this section. In step 2310 of the method, the hostcomputer provides user data. In an optional substep (not shown) the hostcomputer provides the user data by executing a host application. In step2320, the host computer initiates a transmission carrying the user datato the UE. The transmission may pass via the base station, in accordancewith the teachings of the embodiments described throughout thisdisclosure. In step 2330 (which may be optional), the UE receives theuser data carried in the transmission.

As described above, the exemplary embodiments provide both methods andcorresponding apparatuses consisting of various modules providingfunctionality for performing the steps of the methods. The modules maybe implemented as hardware (embodied in one or more chips including anintegrated circuit such as an application specific integrated circuit),or may be implemented as software or firmware for execution by aprocessor. In particular, in the case of firmware or software, theexemplary embodiments can be provided as a computer program productincluding a computer readable storage medium embodying computer programcode (i.e., software or firmware) thereon for execution by the computerprocessor. The computer readable storage medium may be non-transitory(e.g., magnetic disks; optical disks; read only memory; flash memorydevices; phase-change memory) or transitory (e.g., electrical, optical,acoustical or other forms of propagated signals-such as carrier waves,infrared signals, digital signals, etc.). The coupling of a processorand other components is typically through one or more busses or bridges(also termed bus controllers). The storage device and signals carryingdigital traffic respectively represent one or more non-transitory ortransitory computer readable storage medium. Thus, the storage device ofa given electronic device typically stores code and/or data forexecution on the set of one or more processors of that electronic devicesuch as a controller.

Although the embodiments and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made herein without departing from the spirit andscope thereof as defined by the appended claims. For example, many ofthe features and functions discussed above can be implemented insoftware, hardware, or firmware, or a combination thereof. Also, many ofthe features, functions, and steps of operating the same may bereordered, omitted, added, etc., and still fall within the broad scopeof the various embodiments.

While not being limited thereto, some example embodiments of the presentdisclosure are provided in an enumerated list below.

Example Embodiments

1. A method (900) in a wireless device (105), operable in a wirelesscommunication network (100), of identifying reference signal resourcesto be used in a transmission by the wireless device, the methodcomprising: receiving (S905) signaling configuring the wireless deviceto use a plurality of reference signal resource groups, each groupcomprising a plurality of reference signal resources; receiving (S910)an indication, in a control channel, of the reference signal resourcesto be used, wherein the reference signal resources to be used includefirst and second reference signal resources selected only from arespective first and second one of the plurality of reference signalresource groups; and using (S915) the first and second reference signalresources in a reference signal transmission to a network node in thenetwork.

2. The method of embodiment 1, wherein the reference signal resourcesare sounding reference signal (SRS) resources.

3. A method in a wireless device, operable in a wireless communicationnetwork, of identifying one or more SRS resources to be used in atransmission by the wireless device, the method comprising: receivingsignaling configuring the wireless device to use a plurality of SRSresource groups, each group comprising a plurality of SRS resources;receiving an indication, in a physical layer downlink control channel,of the SRS resources to be used; determining, from the indication, afirst and a second SRS resource group, wherein the first and second SRSresource groups are selected from the plurality of SRS resource groups;determining from the indication a first SRS resource that is selectedonly from the first SRS resource group; determining from the indicationa second SRS resource that is selected only from the second SRS resourcegroup; and transmitting at least one of: a) SRSs identified by the firstand second SRS resource, and b) a first and a second MIMO layer inaccordance with the transmission of the first and second SRS resources,respectively.

4. The method of embodiment 3, wherein a size of a field used to signalthe indication is determined based on a maximum number of MIMO layersthat the wireless device is configured to transmit, a number of SRSresource groups from which an SRS resource may be selected, and a numberof SRS resources in the plurality of SRS resource groups.

5. A method in a wireless device, operable in a wireless communicationnetwork, of identifying one or more SRS resources to be used in atransmission by the wireless device, the method comprising: receivingsignaling configuring the wireless device to use a plurality of SRSresources; receiving an indication, in a physical layer downlink controlchannel, of the SRS resources to be used; determining from theindication a first and a second SRS resource out of the plurality of SRSresources that should be used in a given transmission, wherein the firstand second SRS resources can be any of the plurality of the SRSresources, except where the first and second SRS resources are the same;and transmitting at least one of: a) SRSs identified by the first andsecond SRS resource, and b) a first and a second MIMO layer inaccordance with the transmission of the first and second SRS resources,respectively.

6. The method of embodiment 5, wherein the first and second SRSresources are each identified within the plurality of SRS resources by afirst and second index, respectively; and the step of determining fromthe indication a first and a second SRS resource further has the furtherexception that the first index and second index are selected in a singlefixed order, the single fixed order being one of: a) the first index isalways greater than the second index, and b) the first index is alwaysless than the second index.

7. A method in a wireless device, operable in a wireless communicationnetwork, of identifying one or more SRS resources to be used in atransmission by the wireless device, the method comprising: receivingsignaling configuring the wireless device to use a first one of aplurality of SRS resource groups, the first SRS resource groupcomprising a plurality of SRS resources; receiving an indication, in aphysical layer downlink control channel, of an SRS resource to be used;determining from the indication a first SRS resource that is selectedonly from the first SRS resource group; transmitting at least one of: a)an SRS identified by the first SRS resource, and b) a MIMO layer inaccordance with the transmission of the first SRS resource.

8. A method (1100) in a network node, of configuring reference signaltransmission settings in a wireless device operable in a wirelesscommunication network, the method comprising: determining (S1105) atotal number of possible reference signal states based on a grouping ofreference signal resources into reference signal resource groups, thegrouping being configured such that only one reference signal resourceis selectable from each reference signal resource group for use in atransmission; determining (S1110) a mapping of different combinations ofreference signal indication bits to respective ones of the possiblereference signal states; signaling (S1115) the mapping to the wirelessdevice; determining (S1120) one or more preferred reference signalresources for an UL transmission from a wireless device; and signaling(S1125), to the wireless device, reference signal indication bits thatare mapped by the mapping to an SRI state corresponding to the one ormore preferred reference signal resources.

9. The method of embodiment 8, wherein determining a total number ofpossible SRI states based on the grouping of SRS resource groupsincludes fixing an ordering by which SRS resources are mapped to MIMOlayers, thereby restricting the total number of possible SRI states.

10. The method of embodiment 8, wherein determining a total number ofpossible SRI states based on the grouping of SRS resource groupsincludes allowing for SRS resources to be mapped to MIMO layers in anyof a plurality of desired orders.

11. The method of any of embodiments 8-10, wherein the reference signalresources are sounding reference signal (SRS) resources.

12. A wireless device (105, 200) for facilitating communications in awireless communication network (100) by obtaining an indication ofreference signal resources to be used, the wireless device comprisingprocessing circuitry configured to perform the steps of any ofembodiments 1-7.

13. A network node (110, 300) for configuring a reference signalresource in the wireless communication network (100), the network nodecomprising processing circuitry configured to perform the steps of anyof embodiments 8-11.

14. A user equipment (UE) (200) for facilitating communications in awireless communication network (100) by obtaining an indication of areference signal resources to be used, the UE comprising: an antenna(220) configured to send and receive wireless signals; a transceiver(215) connected to the antenna and to processing circuitry (205), andconfigured to condition signals communicated between the antenna and theprocessing circuitry; the processing circuitry being configured toperform the steps of any of embodiments 1-7.

15. A communication system including a host computer comprising:processing circuitry configured to provide user data; and acommunication interface configured to forward the user data to acellular network for transmission to a wireless device, wherein thecellular network comprises a network node having: a) a communicationinterface configured to receive the user data; b) a radio interfaceconfigured to interface with a wireless device to forward the user datato the wireless device; and c) processing circuitry configured toperform the steps of any of embodiments 8-11.

16. The communication system of any of the previous embodiment furtherincluding the network node.

17. The communication system of any of the previous 2 embodiments,further including the wireless device, wherein the wireless device isconfigured to communicate with the network node.

18. The communication system of any of the previous 3 embodiments,wherein: the processing circuitry of the host computer is configured toexecute a host application, thereby providing the user data; and thewireless device comprises processing circuitry configured to execute aclient application associated with the host application.

19. A method implemented in a communication system including a hostcomputer, a network node and a wireless device, the method comprising:at the host computer, providing user data; and at the host computer,initiating a transmission carrying the user data to the wireless devicevia a cellular network comprising the network node, wherein the networknode performs the steps of any of embodiments 1-16.

20. The method of the previous embodiment, further comprising, at thenetwork node, transmitting the user data.

21. The method of any of the previous 2 embodiments, wherein the userdata is provided at the host computer by executing a host application,the method further comprising, at the wireless device, executing aclient application associated with the host application.

22. A communication system including a host computer and a wirelessdevice, the host computer comprising: processing circuitry configured toprovide user data; and a communication interface configured to forwarduser data to a cellular network for transmission to a wireless device,wherein the wireless device comprises a transceiver and processingcircuitry, the wireless device's components being configured to performthe steps of any of embodiments 1-7.

23. The communication system of the previous embodiment, wherein thecellular network further includes a network node configured tocommunicate with the wireless device.

24. The communication system of any of the previous 2 embodiments,wherein: the processing circuitry of the host computer is configured toexecute a host application, thereby providing the user data; and thewireless device's processing circuitry is configured to execute a clientapplication associated with the host application.

25. A method implemented in a communication system including a hostcomputer, a network node, and a wireless device, the method comprising:at the host computer, providing user data; and at the host computer,initiating a transmission carrying the user data to the wireless devicevia a cellular network comprising the network node, wherein the wirelessdevice performs the steps of any of embodiments 1-7.

26. The method of the previous embodiment, further comprising at thewireless device, receiving the user data from the network node.

3GPP Contribution

The following description provides examples of how certain aspects ofthe embodiments described herein could be implemented within theframework of a specific communication standard. In particular, thefollowing examples provide a non-limiting example of how the embodimentsdescribed herein could be implemented within the framework of a 3GPP RANstandard. The changes described by the examples are merely intended toillustrate how certain aspects of the embodiments could be implementedin a particular standard. However, the embodiments could also beimplemented in other suitable manners, both in the 3GPP Specificationand in other specifications or standards.

Title: UL MIMO for Non-Codebook Based Transmission

1—INTRODUCTION

In RAN1-NRAH3, the following agreements were reached online and offline:

The following were agreed in RAN1#90: 1) For PUSCH precoderdetermination in non-codebook-based UL MIMO, support Alt.1, (i.e., atleast SRI(s) only without TPMI indication in the UL grant) for widebandindication. Note: The gNB should only signal SRI(s) such that the ULprecoding transmission inferred from the signaled SRI(s) can besimultaneously conducted by the UE. FFS details. FFS: If sub-bandindication is supported, down-select Alt. 1-3 for it. 2) Specify UEcapability identifying if UL MIMO capable UE can support coherenttransmission across its transmit chains. FFS: if UE capabilityidentifies if coherent transmission is supported on all of, vs. none of,vs. on a subset, of its transmit chains. FFS: how UL MIMO precodingdesign takes into account the above capability.

While the following were agreed in offline discussions in RANI NR AH#3[1]: For non-codebook based transmission, a total of up to 4 SRS portscan be indicated using SRI(s). Note: For non-codebook based precoding,each SRS resource contains one port.

In this contribution, we discuss non-codebook based UL transmission andpresent some further details on SRI indication. In particular, weaddress the open issue of how the UE should signal SRI(s) such that theUL precoding inferred from the SRI(s) can be simultaneously conducted bythe UE, how SRI signaling should take this into account, as well as theneed for frequency selective signaling of SRI.

2—NON-CODEBOOK BASED UL TRANSMISSION

SRS resources can be narrow band and hence only occupy parts of theentire frequency band. However, the SRI(s) determining the preferred SRSresource(s) should be considered as wideband, which means that the SRIshould be applied to the entire bandwidth of the corresponding PUSCHtransmission. For instance, if wideband precoding of the SRS resource isused, the UE simply applies that same precoding for the entire PUSCHallocation. If frequency-selective precoding of the SRS resource isused, the UE shall not be expected to be scheduled on a resourceallocation where it has not previously transmitted an SRS.

Frequency selective UL closed loop precoding has not been shown so farto provide substantial gains, at least for codebook based precoding [2][3] [4]. Reciprocity based high resolution precoding may have additionalpotential for gain, and could also avoid extra overhead for frequencyselective SRI. If full reciprocity cannot be utilized, frequencyselective precoding could be enabled for non-codebook based ULtransmissions by using frequency selective SRI. However, this will alsolead to increased overhead signaling, so further studies will be neededto evaluate the performance gain vs. overhead of such schemes.

Proposal 1: Further study the need for frequency selective SRI,considering performance gain vs. overhead of non-codebook based ULtransmission.

Some UEs might not have calibrated (or only partly calibrated) radiochains which means that the relative phase of the transmit chains is notknown by the UE. In this case precoding (i.e. coherent transmission)will be difficult to apply in a useful manner. Consequently, it wasagreed in RAN1#90 to support a UE capability identifying if a UL MIMOcapable UE can support coherent transmission across its transmit chains.When the UE is not capable of transmitting coherently on any of its Txchains, it is preferred that the UE distributes one SRS resource perantenna arrangement, corresponding to a unit matrix for the Digitalprecoder matrix seen in FIG. 25. The TRP can then select which antennaarrangements that should be used for UL transmissions by reporting oneor several SRIs, where one layer is applied per SRI.

3—SRS RESOURCE GROUPS

Concepts for UL beam management (i.e. beam management based on ULreference signals) are currently being developed for NR to control thebeam (or more correctly the effective antenna pattern) for a respectiveUE antenna subset. It is expected that UL beam management is performedby letting the UE transmit different SRS resources in different UEantenna subset beams, which the TRP performs RSRP measurements on andsignals back the SRI(s) corresponding to the SRS resource(s) withhighest RSRP value(s). If a multi-antenna subset UE is scheduled for SRStransmission of multiple beams from each of the multiple antennasubsets, the TRP and UE need to have a mutual agreement of whichcombinations of SRS resources can be transmitted simultaneously from thedifferent antenna subsets. Otherwise the TRP could select SRS resourcesthat could not be transmitted simultaneously, such as when the SRSresources correspond to different switched analog beams in the sameantenna subset. The note to the agreement from RAN1#90 for signalingmultiple SRIs (below) addresses this issue but does not conclude on howit should be done: Note: The gNB should only signal SRI(s) such that theUL precoding transmission inferred from the signaled SRI(s) can besimultaneously conducted by the UE.

One way to solve this is to identify groups of SRS resources, where onlyone of the resources in an SRS resource group can be transmitted at atime. The one resource from each of the SRS resource groups can betransmitted simultaneously with each of the other selected SRS resourcesfrom the other groups. Given the knowledge of the number of SRS resourcegroups, and which SRS resources are in the groups, the TRP can determinewhich SRS resources it can instruct the UE to transmit when multipleSRIs are signaled. One example will be given below:

Assume a UE with two antenna subsets (e.g., panels) (AntennaSubset/Panel A and Antenna Subset/Panel B), where each antenna subsethas four analog beams (A1-A4 and B1-B4), as illustrated in FIG. 5. TheUE will start with signaling to the TRP, in UE capabilities, that it hastwo SRS resource groups, where each SRS resources group consists of fourSRS resources. For example, a total of SRS resources could beconfigured, where SRS resources 1-4 could belong to a first SRS resourcegroup (corresponding to antenna subset A) and SRS resources 5-8 couldbelong to a second SRS resource group (corresponding to antenna subsetB). During a UE TX beam sweep procedure (i.e. U3), the TRP can triggerthese 8 SRS resources (by an indication in an aperiodic SRS transmissionrequest) and the TRP will know the SRS resources that can and cannot betransmitted simultaneously given the SRS grouping. The TRP can thenperform measurements on the eight transmitted SRS resources, determinethe best SRS resource for each SRS resource group and signal thecorresponding SRIs back to the UE. Note that each SRS resource canconsist of one or several SRS ports, hence the procedure can be appliedfor both non-codebook based (single SRS port per SRS resource) andcodebook based UL transmissions (one or several SRS ports per SRSresource). However, note that, for non-codebook based UL transmissionwhere each SRS resource is allowed to be precoded over multiple antennaports, the SRS precoding in this case (i.e. when UL beam management ispresent) should not be applied over antenna ports belonging to differentantenna subsets (because then the mutual agreement that certain SRSresource only belongs to a certain antenna subset is broken).

We note that the notion of an SRS resource group here serves a similarpurpose to DMRS port groups defined for the NR downlink and to the SRSport group proposed in [5]. Given that an SRI refers to an SRS resource,and since an SRS antenna port group would seem to imply some selectionor subdivision within one SRS resource, ‘SRS resource group’ seems to bemore appropriate to describe the intended behavior.

Proposal 2: SRS resource groups are defined, where a UE can be assumedto be able to transmit only one SRS resource in an SRS resource group ata time, and where a UE can simultaneously transmit one SRS resource fromeach of multiple SRS resource groups.

4—UTILIZING SRS RESOURCE GROUPS IN SRI INDICATION

To indicate multiple SRI(s) in the DCI, one option is to use a size-Nbitmap, where N is the number of SRS resources (corresponding to themaximum rank) and each bit indicates if the SRS resource shall be usedto transmit a PUSCH layer or not. However, this is not a very efficientway of signaling which wastes DCI overhead.

Another option is to, for each rank, jointly indicate which SRSresources shall be used, and then jointly encode TRI and the multipleSRI(s). In this case, the SRI signaling from the TRP to the UE consistsof indicating

$S_{T} = {{\sum\limits_{L = 1}^{L_{{ma}\; x}}S_{L}} = {\sum\limits_{L = 1}^{L_{m\; {ax}}}\begin{pmatrix}N \\L\end{pmatrix}}}$

possible SRI states where

$S_{k} = \begin{pmatrix}N \\k\end{pmatrix}$

is the number of combinations of N values taken k at a time, and N isthe number of SRS resources, L the transmission rank, and L_(max) themaximum transmission rank the UE is capable of. For example, with N=8and L_(max)=2, then the total possible number of SRI states

$S_{T} = {{S_{1} + S_{2}} = {{\begin{pmatrix}8 \\1\end{pmatrix} + \begin{pmatrix}8 \\2\end{pmatrix}} = {{8 + 28} = 36.}}}$

This means that 6 bits are required to indicate the chosen SRI state tothe UE, compared with N=8 bits if the size-N bitmap approach was used.

Further reductions in SRI overhead are possible by taking into accountconstraints on SRS and/or PUSCH MIMO layer transmission. By way ofexample, assume there is a UE with two antenna subsets (e.g., panels)and four analog beams per antenna subset as illustrated in FIG. 5. Insuch a case, many of the possible SRI states will not be allowed becauseonly one SRS resource from each SRS resource group can be selected.Hence, in this case it is preferred to do a mapping between the possibleSRI states and the SRI signalling bits in order to reduce the overhead.For instance, the DCI signalling could indicate one of

$\quad\begin{pmatrix}M \\L\end{pmatrix}$

states, indicating which of the M SRS resource groups are used totransmit L layers, and then the SRS resource to be used in each selectedSRS Resource group could be indicated. For example, if there are 4 SRSresources per group, then 4 states are needed to select a resource froma group. Then with M=2 resource groups and at most L_(max)=2 layers,

$S_{T} = {{S_{1} + S_{2}} = {{{\begin{pmatrix}2 \\1\end{pmatrix} \cdot 4} + {\begin{pmatrix}2 \\2\end{pmatrix} \cdot 4 \cdot 4}} = 24}}$

total states, so 5 bits could be used to signal SRI given that SRSgrouping is taken into account when signalling SRI in this case.

Observation 1: Overhead for SRI signalling can be reduced by consideringthe SRS resource groups during SRI signalling

Proposal 3: Take into account SRS resource grouping when signallingmultiple SRI indications in DCI

5—CONCLUSIONS

In this contribution, we have discussed non-codebook based ULtransmission and further details on SRI indication. In particular, weaddress the open issue of how the UE should signal SRI(s) such that theUL precoding inferred from the SRI(s) can be simultaneously conducted bythe UE, how SRI signaling should take this into account, as well as theneed for frequency selective signaling of SRI. Our analysis led to thefollowing observation and proposals:

Observation 1: Overhead for SRI signalling can be reduced by consideringthe SRS resource groups during SRI signaling.

Proposal 1: Further study the need for frequency selective SRI,considering performance gain vs. overhead of non-codebook based ULtransmission.

Proposal 2: SRS resource groups are defined, where a UE can be assumedto be able to transmit only one SRS resource in an SRS resource group ata time, and where a UE can simultaneously transmit one SRS resource fromeach of multiple SRS resource groups.

Proposal 3: Take into account SRS resource grouping when signallingmultiple SRI indications in DCI.

6—REFERENCES

-   R1-1716921, “Summary of offline discussion on UL MIMO Open Issues”,    Ericsson, 3GPP TSG RAN WG1 NR#3, Nagoya, Japan, Sep. 18-21, 2017-   R1-1708669, “UL MIMO procedures for codebook based transmission”,    Ericsson, 3GPP TSG RAN WG1 Meeting #89, Hangzhou, P.R. China, May    15-19, 2017-   R1-1711008, “UL MIMO procedures for codebook based transmission”,    Ericsson, 3GPP TSG RAN WG1 Meeting #89 adhoc 2, Qingdao, P.R. China,    Jun. 27-30, 2017-   R1-1714271, “UL MIMO for codebook based transmission”, Ericsson,    3GPP TSG RAN WG1 Meeting #90, Prague, Czech Republic, Aug. 21-25,    2017-   R1-1709735, “Way Forward on Uplink Multi-panel and Multi-TRP    operation”, Intel et. al., 3GPP TSG RAN WG1 Meeting #89, Hangzhou,    P.R. China, May 15-19, 2017

LIST OF ABBREVIATIONS

-   -   TRP—Transmission/Reception Point    -   UE—User Equipment    -   NW—Network    -   BPL—Beam pair link    -   BLF—Beam pair link failure    -   BLM—Beam pair link monitoring    -   BPS—Beam pair link switch    -   RLM—radio link monitoring    -   RLF—radio link failure    -   PDCCH—Physical Downlink Control Channel    -   RRC—Radio Resource Control    -   CRS—Cell-specific Reference Signal    -   CSI-RS—Channel State Information Reference Signal    -   RSRP—Reference signal received power    -   RSRQ—Reference signal received quality    -   gNB—NR base station    -   PRB—Physical Resource Block    -   RE—Resource Element

1. A method in a wireless device, operable in a wireless communication network, of identifying a plurality of SRS resources, the method comprising: receiving signaling configuring the wireless device with a plurality of SRS resources; receiving an indication, in a physical layer downlink control channel, of SRS resources; determining from the indication at least a first and a second SRS resource out of the plurality of SRS resources, wherein the first and second SRS resources are not the same; and transmitting first and second MIMO layers that are mapped to the first and second SRS resources, respectively.
 2. The method of claim 1, wherein determining the at least first and second SRS resources includes identifying the first and second SRS resources from among the plurality of SRS resources by a first and second index, respectively; and wherein the first and second indexes further indicate an order in which the first and second SRS resources are to be mapped to the first and second MIMO layers.
 3. The method of claim 2, wherein the first and second MIMO layers are ranked by quality such that the first MIMO layer is of higher quality than the second MIMO layer and the first MIMO layer is mapped to by a lower one of the first and second indexes.
 4. The method of claim 2, wherein the first and second MIMO layers are ranked by quality such that the first MIMO layer is of higher quality than the second MIMO layer and the first MIMO layer is mapped to by a higher one of the first and second indexes.
 5. The method of claim 1, wherein the wireless device determines the first and second SRS resources according to table, wherein the table includes only one entry for each possible ordering of a combination of SRS resources
 6. The method of claim 1, wherein the signaling configuring the wireless device with a plurality of SRS resources indicates groupings of the plurality of SRS resources into a plurality of SRS resource groups, each group comprising a plurality of SRS resources and wherein the first and second SRS resources are selected from the same SRS resource group.
 7. A user equipment (UE) for facilitating communications in a wireless communication network by obtaining an indication of a reference signal resources to be used, the UE comprising: an antenna configured to send and receive wireless signals; and a transceiver connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry, the processing circuitry being configured to carry out a method comprising: receiving signaling configuring the wireless device with a plurality of SRS resources; receiving an indication, in a physical layer downlink control channel, of SRS resources to be used; determining from the indication at least a first and a second SRS resource out of the plurality of SRS resources that should be used in a transmission, wherein the first and second SRS resources are not the same; and transmitting first and second MIMO layers that are mapped to the first and second SRS resources, respectively.
 8. The UE of claim 7, wherein determining the at least first and second SRS resources includes identifying the first and second SRS resources from among the plurality of SRS resources by a first and second index, respectively; and wherein the first and second indexes further indicate an order in which the first and second SRS resources are to be mapped to the first and second MIMO layers.
 9. The UE of claim 7, wherein the wireless device determines the first and second SRS resources according to table, wherein the table includes only one entry for each possible ordering of a combination of SRS resources
 10. The UE of claim 7, wherein the signaling configuring the wireless device with a plurality of SRS resources indicates groupings of the plurality of SRS resources into a plurality of SRS resource groups, each group comprising a plurality of SRS resources and wherein the first and second SRS resources are selected from the same SRS resource group.
 11. A method in a network node, operable in a wireless communication network, of identifying a plurality of SRS resources to be used in a transmission by a wireless device, the method comprising: transmitting signaling configuring the wireless device with a plurality of SRS resources; transmitting an indication, in a physical layer downlink control channel, of SRS resources to be used in a transmission, the indicated SRS resources including at least a first and a second SRS resource out of the plurality of SRS resources, wherein the first and second SRS resources are not the same; and receiving first and second MIMO layers that are mapped to the first and second SRS resources, respectively.
 12. The method of claim 11, wherein the first and second SRS resources are each indicated from among the plurality of SRS resources by a first and second index, respectively; and wherein the first and second indexes further indicate an order in which the first and second SRS resources are to be mapped to the first and second MIMO layers.
 13. The method of claim 12, wherein the first and second MIMO layers are ranked by quality such that the first MIMO layer is of higher quality than the second MIMO layer and the first MIMO layer is mapped to by a lower one of the first and second indexes.
 14. The method of claim 12, wherein the first and second MIMO layers are ranked by quality such that the first MIMO layer is of higher quality than the second MIMO layer and the first MIMO layer is mapped to by a higher one of the first and second indexes.
 15. The method of claim 11, wherein the indication of SRS resources to be used indicates an entry of a table, wherein the table includes only one entry for each possible ordering of a combination of SRS resources.
 16. The method of claim 11, wherein the signaling configuring the wireless device with a plurality of SRS resources indicates groupings of the plurality of SRS resources into a plurality of SRS resource groups, each group comprising a plurality of SRS resources and wherein the first and second SRS resources are selected from the same SRS resource group.
 17. A network node for configuring a reference signal resource in the wireless communication network (100), the network node comprising: an antenna configured to send and receive wireless signals; and a transceiver connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry, the processing circuitry being configured to carry out a method comprising: transmitting signaling configuring the wireless device with a plurality of SRS resources; transmitting an indication, in a physical layer downlink control channel, of SRS resources to be used in a transmission, the indicated SRS resources including at least a first and a second SRS resource out of the plurality of SRS resources, wherein the first and second SRS resources are not the same; and receiving first and second MIMO layers that are mapped to the first and second SRS resources, respectively.
 18. The network node of claim 17, wherein the first and second SRS resources are each indicated from among the plurality of SRS resources by a first and second index, respectively; and wherein the first and second indexes further indicate an order in which the first and second SRS resources are to be mapped to the first and second MIMO layers.
 19. The network node of claim 17, wherein the wireless device determines the first and second SRS resources according to table, wherein the table includes only one entry for each possible ordering of a combination of SRS resources
 20. The network node of claim 17, wherein the signaling configuring the wireless device with a plurality of SRS resources indicates groupings of the plurality of SRS resources into a plurality of SRS resource groups, each group comprising a plurality of SRS resources and wherein the first and second SRS resources are selected from the same SRS resource group. 